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The present invention relates generally to devices for terminating transmission lines and buses, and more specifically to line terminators configured to provide adjustable termination impedance.
Line terminators are commonly used in computers and other electronic systems and devices for terminating transmission lines and buses to preserve the integrity of signals or data carried by the transmission lines and buses. For example, an electronic system may include one or more buses such as a Small Computer System Interface (SCSI) bus having one or more SCSI-compatible devices or peripherals (e.g., disk drives, CD-ROM drives, optical drives, and/or tape units) connected thereto. The SCSI devices are typically accessed through a SCSI controller, which is also connected to the SCSI bus. The SCSI controller employs respective device drivers to generate signals for controlling the SCSI devices on the SCSI bus. In order to maintain the integrity of the control signals and data carried by the SCSI bus, the bus is normally terminated at each end by a respective line terminator device. Each line terminator is configured to prevent reflections at the end of the SCSI bus, which may distort the signals carried by the bus and/or cause data errors to appear on the bus.
A conventional line terminator device for terminating transmission lines and buses may be configured to provide either xe2x80x9cpassivexe2x80x9d termination or xe2x80x9cactivexe2x80x9d termination. For example, a line terminator for terminating a SCSI bus may be configured to provide an impedance of about 220 xcexa9 to Terminal Power (e.g., 5 V) and about 330 xcexa9 to ground potential for passive termination. Alternatively, a line terminator may employ one or more voltage regulators and resistors for active termination of a SCSI bus carrying data at high data rates.
One drawback of conventional line terminator devices is that they often fail to provide optimal termination impedance when the line impedance is variable or not well defined during the design of an electronic system or device. This is because such line terminators are typically configured for terminating transmission lines and buses having precisely known line impedance values. For example, the impedance of a SCSI bus may vary based on the number and/or type of SCSI devices or peripherals connected to the bus. Because conventional line terminators are typically configured to match known line impedance values, when the line impedance changes, optimal termination impedance frequently cannot be achieved.
It would therefore be desirable to have a line terminator device for providing optimal termination impedance for a transmission line or bus. Such a line terminator would be capable of optimally terminating a transmission line or bus even if the impedance of the transmission line or bus is variable or not well defined.
In accordance with the present invention, a line terminator device is provided that can optimally terminate a transmission line or bus even if the line impedance is variable or not well defined. Benefits of the presently disclosed line terminator are achieved by making the line terminator programmable, thereby allowing the line terminator to be programmably configured for providing optimal termination impedance for the transmission line or bus.
In one embodiment, the line terminator device comprises a programmable multi-line active terminator configured to terminate at least one transmission line or bus. The line terminator is operative to provide programmable termination impedance and bias for a plurality of lines on the bus. The line terminator may be uniquely addressed and programmed via address and control signals carried by one or more of the lines on the bus. Alternatively, the line terminator may be connected to one or more lines separate from the bus, and subsequently addressed and programmed via address and control signals carried by these separate lines. The line terminator employs a plurality of switches for setting its unique address. The line terminator is configured to detect what type of bus it is terminating and what types of devices are connected to the bus. The line terminator includes a mechanism for programmably adjusting the termination impedance and bias for the lines on the bus based on the bus type, the types of devices connected to the bus, and/or the control signals carried by the bus or the separate lines.
By providing a programmable line terminator device that can supply programmable termination impedance and bias for a plurality of transmission lines having line impedance values that may be variable or not well defined, increased signal bandwidth, reduced signal distortion, and high data rates with reduced error can be achieved.
Other features, functions, and aspects of the invention will be evident from the detailed description of the invention that follows.